Glucagon-like peptide 1 (GLP-1), a hormone mainly produced in a nutrient-dependent manner by gastrointestinal endocrine L cells (see, for example, Parker et al., 2010, Expert Rev Mol Med 12:e1), enhances glucose-dependent insulin secretion and inhibits food intake, gastric emptying, and glucagon release, thus promoting the maintenance of normal glucose homeostasis (see, for example, Lauffer et al., 2009, Diabetes 58, 1058-1066; Gribble, 2008, Diabet Med 25, 889-894). A small, but significant, defect in mixed meal and oral glucose load stimulated GLP-1 secretion has been observed in Type 2 Diabetes (T2DM) (see for example, Mannucci et al., 2000, Diabet Med 17, 713-719; Vilsboll et al., 2001, Diabetes 50, 609-613). In Type 2 diabetic patients, chronic administration of native GLP-1, via continuous infusion or repeated subcutaneous injection, reduces fasting and postprandial blood glucose and decreases glycosylated hemoglobin (HbA1c) in association with a modest, but significant weight loss (see, for example, Zander et al., 2002, Lancet 359, 824-830; Meneilly et al., 2003, Diabetes Care 26 2835-2841). The short half-life of native GLP-1, due to rapid inactivation mainly catalyzed by dipeptidyl-peptidase-4 (DDP-4), has engendered interest in the development of more stable longer-acting GLP-1 receptor agonists to be used as hypoglycemic drugs for the treatment of T2DM. Exendin-4 (Ex-4), a peptide isolated from the salivary secretion of the Gila monster, is a potent GLP-1 receptor agonist, which, because of its molecular structure, is considerably more resistant than native GLP-1 to degradation by DPP-4 (see, for example, Neumiller, 2009, J Am Pharm Assoc 49 (suppl. 1, S16-S29). Exenatide (the synthetic form of exendin-4, brand name BYETTA®) significantly improves glycemic control and causes weight loss in type 2 diabetic patients (see, for example, Madsbad, 2009, Best Pract Res Clin Endocrinol Metab 23, 463-477). Exenatide, which has been approved for the treatment to Type 2 Diabetes, requires twice daily subcutaneous administration.
Gene therapy offers the possibility of more stable long-term expression for the treatment of many chronic diseases, including T2DM (Srivastava, 2008, J Cell Biochem 105, 17-24). Recently, adenoviral and plasmid-based vectors have been used to express GLP-1 receptor agonists in several tissues, but have not resulted in long-term effects, as a result of either low or transient expression (see, for example, Voutetakis et al., 2010, Endocrinology 151, 4566-4572; Kumar et al., 2007, Gene Ther 14, 162-172; Liu et al., 2010, Biochem Biophys Res Commun 403, 172-177; Samson et al., 2008, Mol Ther 16, 1805-1812 (erratum in Mol Ther 17, 1831); Lee et al., 2008, J Gene Med 10, 260-268; Choi et al., 2005, Mol Ther 12, 885-891; Lee et al., 2007, Diabetes 56, 1671-1679). While effective in animal models, the inherent risk profile related to systemic delivery of vectors supported site-specific gene therapeutic approaches as an appealing alternative.
Recently, adeno-associated viruses (AAVs) have advanced to the forefront of gene therapy, due to their ability to achieve long-term transgene expression in vivo and low immunogenicity (see, for example, Sumner-Jones et al., 2006 Gene Ther 13, 1703-1713; Stieger et al., 2006, Mol Ther 13, 967-975; Niemeyer et al., 2009, Blood 113, 797-806; Daya et al., 2008, Clin Microbiol Rev 21, 583-593). Several Phase I/II clinical trials support a good overall safety profile for AAV vectors and little associated toxicity in humans (see, for example, Mandel, 2010 Curr Opin Mol Ther 12, 240-247; Bainbridge et al., 2008, N Engl J Med 358, 2231-2239; Moss et al., 2004, Chest 125, 509-521; Diaz-Nido, 2010, Curr Opin Investig Drugs 11, 813-822; Simonelli et al., 2010, Mol Ther 18, 643-650). Over 100 AAV isolates have been reported; biochemical and molecular characterization suggests that some exhibit different tissue tropism, persistence, and transduction efficiency (see, for example, Kwon et al., 2008, Pharm Res 25, 489-499). Among AAVs, serotype 5 (AAV5) has demonstrated enhanced gene transfer activity in lung, eye and CNS as well as rodent salivary glands (SG) (see, for example, Katano et al., 2006, Gene Ther 13, 594-601.
Salivary glands are recognized as a useful depot organ in gene therapy, having several important features of other endocrine glands, such as high protein production and ability to secrete proteins into the bloodstream (see, for example, Voutetakis et al., 2005, J Endocrinol 185, 363-372). It has been previously reported that salivary glands are able to produce pharmacological levels of growth hormone and parathyroid hormone following transduction with recombinant viral vectors (see, for example, He et al., 1998, Gene Ther 5, 537-541; Adriaansen et al., 2011, Hum Gene Ther 22, 84-92).
There still remains a need for an effective and safe composition to protect subjects from diabetes or obesity.